A Drug Enforcement Administration administrative law judge, calling marijuana "one of the safest therapeutically active substances known to man," recommended yesterday that the drug be made legally available for some medical purposes, including treatment of cancer patients.

If adopted, the opinion by Judge Francis L. Young would mean that doctors could prescribe marijuana--a fundamental change in the drug's legal status that some specialists said could aid tens of thousands of patients suffering from nausea-inducing chemotherapy and muscle spasms of multiple sclerosis.

The opinion is not likely to have any immediate effect because DEA Administrator John C. Lawn is considered almost certain to reject Young's conclusions (he did). Nevertheless, coming after a 16- year legal battle, the 69-page ruling marks the first time a government official has accepted a medical role for the country's widely used illicit drug.

"The evidence in this record clearly shows that marijuana has been accepted as capable of relieving the distress of great numbers of very ill people, and doing so with safety under medical supervision," Young wrote. "It would be unreasonable, arbitrary and capricious for DEA to continue to stand between those sufferers and the benefits of this substance in light of the evidence in this record."

The long-awaited ruling was immediately criticized by DEA lawyers and antidrug groups who said it would send a confusing message at a time the federal government is attempting to wage a war on drugs. DEA officials also said the ruling ran counter to the body of accepted medical opinion. "This totally ignores the bulk of the medical evidence," said Stephen E. Stone, associate counsel of DEA, which had fought changing marijuana's classification. "The judge seems to hang his hat on what he calls a 'respectable minority of physicians.' What percent are you talking about? One half of 1 percent? One quarter of 1 percent?

"From our point of view, marijuana has not been established as a safe and effective drug," Stone added.

Young's ruling, which cites medical researchers from Harvard, New York University and other leading medical schools, comes in the form of a recommendation to Lawn to change the status of marijuana under the 1970 Controlled Substance Act. Ever since the act was passed, marijuana has been classified with heroin and LSD as a Schedule 1 controlled substance, which means it is an illegal drug with no known medical use.

Young recommends that Lawn use discretionary authority to make marijuana a Schedule 2 substance. This means it would become a drug--like morphine and cocaine--that, while still unavailable to the general public, can be prescribed by doctors for limited purposes.

A DEA spokesman and said yesterday that Lawn would not comment on the ruling until he has a chance to review it. Even if he rejects the recommendation, however, lawyers for the National Organization for the Reform of Marijuana Laws (NORML) and other pro-marijuana groups said Young's ruling would provide a powerful evidence to overturn a rejection in federal court.

"This is the most significant victory that one can imagine," said Robert C. Randall, president of the Alliance for Cannabis Therapeutics, a group that joined with NORML and the Drug Policy Foundation in petitioning DEA for the ruling. "For the first in over half a century, the federal government is viewing marijuana in a rational context . . . not just saying it's something evil."

In his opinion, Young cited a number of medical experts and patients as a basis for his conclusion that marijuana's medical use was "clear beyond any question" Their testimony showed that marijuana helped suppress nausea and vomiting experienced by chemotherapy patients, was a "highly successful appetite stimulant" and was widely--if illicitly--used in some hospitals.

"This successful use of marijuana has given many cancer chemotherapy patients a much more positive outlook on their overall treatment," Young wrote, adding that smoking marijuana was far more effective than taking pills with synthetic THC, the active ingredient in the drug.

Young found similar benefits for using marijuana to control muscle spasms suffered by patients with multiple sclerosis, spasticity and hyperparathyroidism, a painful hormonal disorder that causes bone spurs. But Young rejected permitting marijuana for treatment of glaucoma, saying there is insufficient evidence that many physicians support such a move. At the core of Young's ruling, however, was his conclusion that the dangers of marijuana do not outweigh its medical benefits. While agreeing that marijuana "can be harmful" and "abused," he noted there is still not a documented death caused by the drug. "In strict medical terms, marijuana is far safer than many foods we commonly consume," he wrote.